Short-term results of Na131I treatment of hyperthyroidism evaluated using an extended dosimetric method

Theoretical aspects on the use of single-time-point dosimetry for radionuclide therapy

Objective: This study considers the error distributions for time-integrated activity (TIA) of single-time-point (STP) methods for patient-specific dosimetry in radionuclide therapy.Approach: The general case with the same pharmaceutical labelled with different radionuclides for imaging and therapy are considered for a mono-exponential time-activity curve. Two methods for STP dosimetry, both based on the combination of one activity estimate with the population-mean effective decay constant, are investigated. The cumulative distribution functions (CDFs) and the probability density functions for the two methods are analytically derived for arbitrary distributions of the biological decay constant. The CDFs are used for determining 95 % coverage intervals of the relative errors for different combinations of imaging time points, physical decay constants, and relative standard deviations of the biological decay constant. Two examples, in the form of kidney dosimetry in [¹⁷⁷Lu]Lu-DOTA-TATE therapy and tumour dosimetry for Na[¹³¹I]I therapy for thyroid cancer with dosimetry based on imaging of Na[¹²⁴I]I, are also studied in more detail with analysis of the sensitivity with respect to errors in the mean biological decay constant and to higher moments of the distribution.Main results: The distributions of the relative errors are negatively skewed, potentially leading to the situation that some TIA estimates are highly underestimated even if the majority of estimates are close to the true value.Significance: The main limitation of the studied STP dosimetry methods is thereby the risk of large underestimations of the TIA.

A Systematic Review and Meta-Analysis of the Relationship Between the Radiation Absorbed Dose to the Thyroid and Response in Patients Treated with Radioiodine for Graves' Disease

Background: Patients with Graves' disease are commonly treated with radioiodine. There remains controversy over whether the aim of treatment should be to achieve euthyroidism or hypothyroidism, and whether treatments should be administered with standard levels of radioactivity or personalized according to the radiation absorbed doses delivered to the thyroid. The aim of this review was to investigate whether a relationship exists between radiation absorbed dose and treatment outcome. Methods: A systematic review and meta-analysis of all reports published before February 13, 2020, were performed using PubMed, Web of Science, OVID MEDLINE, and Embase. Proportion of patients achieving nonhyperthyroid status was the primary outcome. Secondary outcomes were proportion of patients who were specifically euthyroid or hypothyroid. A random-effects meta-analysis of proportions was performed for primary and secondary outcomes, and the impact of the radiation absorbed dose on treatment outcome was assessed through meta-regression. The study is registered with PROSPERO (CRD42020175010). Results: A total of 1122 studies were identified of which 15, comprising 2303 Graves' disease patients, were eligible for the meta-analysis. A strong association was found between radiation absorbed dose and nonhyperthyroid and hypothyroid outcomes (odds ratio [OR] = 1.11 [95% confidence interval {CI} 1.08-1.14] and OR = 1.09 [CI 1.06-1.12] per 10 Gy increase). Higher rates of euthyroid outcome were found for radiation absorbed doses within the range 120-180 Gy when compared with outside this range (n = 1172, OR = 2.50 [CI 1.17-5.35], p = 0.018). A maximum euthyroid response of 38% was identified at a radiation absorbed dose of 128 Gy. Conclusions: The presented radiation absorbed dose-response relationships can facilitate personalized treatment planning for radioiodine treatment of patients with Graves' disease. Further studies are required to determine how patient-specific covariates can inform personalized treatments.